超导材料Nb_3Ge表面氧化

Oxidation of Nb_3Ge surface

运用密度泛函理论计算了氧(O)在Nb3Ge表面的吸附,结果表明O倾向于吸附在Nb原子周围,并与Nb的电子轨道发生了明显的交叠,O与Nb形成兼具共价键和离子键特性的化学键。利用X射线光电子能谱对自然氧化的Nb3Ge表面进行成分分析发现:氧化层中只存在Nb的氧化物,理论计算结果与实验结果一致。由于O容易与Nb结合,最外层的Nb因逐渐氧化而耗尽,在接触势的驱使下,内部的Nb原子与最外层的Ge原子交换,最终使得Nb与O的形成氧化物在Nb3Ge表面聚集,在该氧化层下面是由于Nb的耗尽而形成的Ge聚集层。

The oxide layer grown on the A15 Nb3Ge surface after exposure to air is found to be mainly Nb2O5 from the observation of X-ray photoelectron spectroscopy,and no germanium oxide is detected.In order to investigate the initial oxidation mechanism of Nb3Ge,the adsorption of O atoms on Nb3Ge surface is performed within density functional theory（DFT）.O atom prefers to bonding with Nb atom,and the bond is both ionic and covalent,which is consistent with the experiment.As the outer Nb oxidizes gradually,the inner Nb atoms begin to exchange with outer Ge atoms with the motivation of the contact potential,therefore niobium oxide congregates on the surface,also there is Ge accumulation under this oxide layer.